INVERSE A: Inverse agonism. Implications for drug design.

• Research unit: EU RFP
• Project number: 96.0325

Key words (English)

G protein-coupled receptors; adrenergic receptors; constitutive activity; inverse agonism

Alternative project number (English)

EU project number: BMH4-CT97-2152

Research programs (English)

EU-programme: 4. Frame Research Programme - 4.2 Agriculture and agroindustry

Short description (English)

See abstract

Further information (English)

Full name of research-institution/enterprise:
Université de Lausanne
Institut de Pharmacologie et de Toxicologie

Partners and International Organizations (English)

Istituto Superiore di Sanità, Rome (I), A.P. Ijzerman, Amsterdam (NL), M. Lohse, Universität Würzburg (D), G. Millligan, University Glasgow (UK), N. Shankley and J. Black, London (UK)

Abstract (English)

During the third and last year of the project, our research mainly focussed on the investigation of the molecular basis underlying inverse agonism at the a1a and a1b-adrenergic receptor (AR) subytpes. As indicated in our last report, we have found that the majority of classical alpha-blockers display profound negative efficacy at both the a1a and a1b-AR subtypes with the exception a group of N-arylpiperazines (REC 15/3039, REC 15/2739 and REC 15/3011) which are inverse agonists at the a1b-AR, but not at the a1a-AR. These drugs are the only compounds identified so far which do not behave as inverse agonists at one of the a1-AR subtypes (Rossier et al., 1999) and have been shown to have fewer cardiovascular effects in vivo as compared to compounds behaving as inverse agonists at both receptors. Preliminary structure-activity relationship analysis of the alpha-blockers provided some interesting suggestions about the structural features of the ligands which might correlate with their inverse agonism and might be useful for drug design.
To further elucidate the molecular mechanisms underlying inverse agonism, we have undertaken the effort of mapping the putative docking sites of inverse agonists and neutral antagonists at the a1-a and a1-b-AR subtypes. Combining site-directed mutagenesis of the receptors and molecular dynamics analysis of their models we have identified a number of aromatic residues conserved in the helical bundle of both receptor subtpyes which might contribute to form their binding pocket. Interestingly, the integrity of the residues forming the binding pocket as well as that of the catechol-binding serines is required to maintain the constitutive activity of the a1-AR subtypes. This supports the hypothesis proposed for the b2-AR that catechol-binding serines of b2-adrenergic receptors control the equilibrium between active and inactive receptor states (Ambrosio et al., 2000).
Among the conserved aromatic residues, a trypthophane on helix 6 seems crucially involved in receptor activation as well as in docking inverse agonists, but not neutral antagonists. Our current working hypothesis is that inverse agonists at the the a1-AR subtypes interact with the fundamental mechanisms underlying agonist-induced receptor activation. This work is still ongoing and will be the object of future publications (Rossier et al., in preparation).

References in databases (English)

Swiss Database: Euro-DB of the
State Secretariat for Education and Research
Hallwylstrasse 4
CH-3003 Berne, Switzerland
Tel. [phone]
Swiss Project-Number: 96.0325